This invention relates to an apparatus for monitoring a machining state of a drill of a machine tool for machining a board or plate to be machined such as a printed board, etc.
Generally, at the time of carrying out a boring or drilling work of a printed board, drills having an extremely fine diameter are used under the existing circumstances. For this reason, there results high percentage of occurrence of breakage during machining. It is therefore indispensable for protection of a printed board to accurately detect such a breakage to stop the operation of the machine tool. Further, it is desirable also from a viewpoint of improvement in the working efficiency to monitor a machining state of the drill at all times.
Meanwhile, conventionally, in the case of detecting a breakage of the drill, e.g., a light emitting element and a light receiving element for an optical fiber are oppositely provided at suitable portions of the circumferential side wall of a through-hole formed in the vertical movement plate of the machine tool, thus to directly detect a breakage of the drill.
However, the method of directly monitoring a breakage of the drill by means of an optical fiber sensor had the drawbacks that according as the diameter of the drill becomes fine, the processing (machining) or assembling accuracy may become extremely bad, and that any erroneous operation may take place by deviation of the optical axis resulting from aged deterioration, an erroneous sensing resulting from chips, or the like.